There has been conventionally known, in a pneumatic tire for an icy/snowy road, a structure having: a plurality of blocks demarcated in a ground contact surface of a tread by main grooves extending in the tread circumferential direction and lateral grooves extending in the tread width direction; and a plurality of sipes formed in the blocks to extend in the tread width direction. Further, in a pneumatic tire for an icy/snowy road, there has been known as a structure of tread rubber what is called “cap-and-base” structure including a base rubber of high hardness and a cap rubber of low hardness provided on the outer side in the tire radial direction of the base rubber in a stacked manner.
According to the structures described above, it is possible to achieve good on-snow performance by ensuring a satisfactorily large groove area by the main grooves and the lateral grooves, as well as good-on ice performance by an edge effect caused by the sipes and a good ground contacting effect caused by the ground contact surface of the tread made of the cap rubber having low hardness.
In this regard, there has been proposed, as a technique of further improving gripping performance of the tire on an icy/snowy road surface, a technique of increasing ground contact pressure at a center portion of the tread by decreasing a radius of curvature of a crown portion of the tire (refer to PTL 1 and PTL 2, for example).